1. Field of the Invention
The invention relates to a video signal processing circuit for performing a signal processing that is useful, for example, to allow a display panel such as a plasma display panel or the like, or a display such as a CRT or the like to display a video image of desired brightness, contrast, color tone, white balance, and so on.
The invention also relates to a color adjusting circuit for performing a color adjusting process to a color video signal, particularly, to color difference signals.
2. Description of Related Art
Japanese Patent Kokai 2-296290 discloses a color adjusting apparatus in which 3-primary color component data is converted to luminance component data and chromaticity component data, the obtained chromaticity component data is further transformed to polar coordinates, a color tone is adjusted by adjusting the level of the polar coordinates component data, and thereafter, the data after the adjustment is inversely converted, thereby returning it to the original 3-primary color component data.
Since the color adjusting apparatus involves the polar coordinates transformation which needs complicated arithmetic operations, a problem is that a circuit construction of the whole apparatus is complicated and the apparatus becomes expensive.
On the other hand, a color display is generally provided with a color adjusting circuit for performing color adjustments of saturation, hue, and the like in order to obtain a desired color display state.
According to conventional color adjusting circuits, however, since the adjusting process is performed to all of the colors in a display image, the color adjustments are performed also to a color component to which the user wants to maintain a present color state. Consequently, a problem exists that it is difficult to adjust the color display to a desired color display state.
The invention has been made to solve the problems and it is an object of the invention to provide a video signal processing circuit which can perform conversion between 3-primary color signals and a luminance signal and color difference signals and also can perform various adjustments to a video signal by a simple circuit construction.
It is another object of the invention to provide a color adjusting circuit of a color video signal which can perform color adjustments such as saturation adjustment and hue adjustment only to a desired color region in a display image.
According to the invention, there is provided a color adjusting circuit of a color video signal for obtaining color adjustment color difference signals by performing a color adjusting process according to a color adjustment signal to color difference signals in the color video signal, comprising: a first coordinates transforming circuit for performing a rotary coordinate transformation to the color difference signals by an amount corresponding to a color designation angle according to a color designation signal, thereby obtaining rotated color difference signals; a region discriminating circuit for discriminating whether the color difference signals exist in the color region shown by the color designation signal in color coordinates or not; a level adjusting circuit for performing a level adjustment according to the color adjustment signal only to the rotated color difference signals obtained based on the color difference signals which were determined to be existing in the color region; and a second coordinates transforming circuit for performing a rotary coordinate transformation to the rotated color difference signals subjected to the level adjustment by the level adjusting circuit by the amount corresponding to the color designation angle in the direction opposite to that in the rotary coordinate transformation and outputting resultant signals as the color adjustment color difference signals.